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Endo/Repro > 03b: Thyroid > Flashcards

03b: Thyroid Flashcards

1
Q

Major secretory product of thyroid gland is (X).

A

X = T4 (thyroxine)

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2
Q

(T4/T3/rT3) are active forms. Which of these are produced exclusively in thyroid gland?

A

T3;

T4 (T3 and rT3 can be produced from T4 in peripheral tissues)

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3
Q

(X) enzymes in peripheral tissues catalyze production of (T3/rT3/T4) from (T3/rT3/T4).

A

X = 5’-deiodinases;
T3 or rT3;
T4

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4
Q

T/F: Most circulating T3 is formed from degradation of T4, not from biosynthesis.

A

True

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5
Q

T4 biosynthesis: two coupled (X) rings form (Y).

A 
X = Tyr
Y = thyronine
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6
Q

TRH is formed in (X) and carried to (Y) cells to induce TSH secretion. Is TRH a clinically useful measurement of thyroid function?

A 
X = PVN of hypothalamus
Y = thyrotropes (of ant pit)

No - conc too low in peripheral circulation

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7
Q

Most important regulator of TRH production:

A

Long-loop negative feedback by T3/T4

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8
Q

List the four hormones, released from (X), that have same alpha and different beta subunits.

A

X = anterior pituitary;

LH, FSH, TSH, hCG

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9
Q

Most negative feedback control regulating Thyroid hormone levels takes place between (thyroid/pituitary) and (pituitary/hypothalamus).

A

Thyroid and pituitary

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10
Q

Within the thyrotrope, (T3/rT3/T4) is the hormone that produces negative feedback effects. Most of it comes from (X).

A

T3;

X = intra-pituitary conversion of T4 to T3

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11
Q

(T3/T4) negative feedback within thyrotrope has which mechanism?

A

T3;

Binds nuclear receptors and inhibits expression of both TSH subunits

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12
Q

List the levels at which glucocorticoids (stimulate/inhibit) thyroid axis.

A

Inhibit;

  1. TRH synthesis
  2. Thyrotrope responsiveness to TRH
  3. Deiodinase activity
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13
Q

Under intense TSH stimulation, you’d expect the thyroid follicle to appear:

A

Hyperplastic (shrunken); colloid undergoing resorption for hormone synthesis

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14
Q

Thyroid hormone biosynthesis requires which two components?

A
  1. Thyroglobulin

2. Iodide

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15
Q

Iodide enters thyroid follicular cell via (X). This is a(n) (uphill/downhill) movement.

A

X = Na/I symporter (NIS)

Uphill (very high iodide conc in cell compared to out)

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16
Q

Which transport proteins/pumps are present on (apical/basal) membrane of thyroid follicular cell to allow iodide entry?

A

Basal;

  1. NIS (symporter)
  2. Na/K Pump (too keep Na low in cell)
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17
Q

T/F: Iodide entry into follicular cell is rate-limiting step of thyroid hormone production.

A

True

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18
Q

TPO (thyroid peroxidase) is key enzyme that catalyzes which steps in thyroid hormone synthesis?

A
  1. Oxidization of iodide (to iodine)
  2. Incorporation into thyroglobulin
  3. Coupling (ex: T2 and T2 to form T4)
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19
Q

Immediately (before/after) exiting (apical/basal) membrane of follicular cell, iodide is (oxidized/reduced) to (X).

A

After; apical;
Oxidized
X = iodine
(by TPO enzyme)

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20
Q

The iodide attaches to (X) residues of thyroglobulin.

A

X = Tyr

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21
Q

Thyroid hormone synthesis: The actions of TPO are mediated by (X), which is generated by (Y).

A 
X = H2O2
Y = NADPH oxidase
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22
Q

Iodide transport across apical membrane of follicular cell is via (X) channel/ATPase/transporter.

A

X = Pendrin (I/Cl antiporter)

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23
Q

Tyrosine organification/iodination yields which products?

A
  1. MIT (T1) or

2. DIT (T2)

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24
Q

Thyroid colloid stores enough organified thyroglobulin for (X) period of time.

A

X = 2-3 months

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25
T/F: When thyroid hormone is needed, biosynthesis of thyroglobulin starts de novo and stored iodide (in colloid) is available.
False - colloid stores months' worth of already organified thyroglobulin
26
Upon stimulation of thyroid gland, follicular cells endocytose (X), which fuse with (Y). Finally, (Z) process forms mature thyroid hormones.
``` X = colloid Y = intracellular lysosomes Z = proteolysis of thyroglobulins ```
27
Thyroid hormone synthesis: following proteolysis in lysosome, (X) enter circulation. What's the fate of the byproducts?
X = mature hormones (T3/T4) MIT, DIT stay in follicular cell and deiodinated (by thyroid deiodinase); recycling
28
Most of the iodide used in thyroid hormone synthesis comes from:
Recycling of MIT, DIT iodides following their deiodination
29
Perchlorate, a competitive inhibitor of NIS transporter, can be administered clinically to treat:
Hyperthyroidism (since it slows down thyroid hormone production)
30
The Wolff-Chaikoff effect is essentially (stimulation/inhibition) of (X) in response to (Y).
Inhibition; X = TPO Y = high circulating iodide
31
The Wolff-Chaikoff effect typically lasts how long? What's the mechanism that causes escape from this effect?
A few days; | Down-regulation of NIS allows thyroid to adjust to high iodide levels (and TPO inhibition is released)
32
About (X) T4 and (Y) T3 are secreted daily.
``` X = 80-100 micrograms Y = 5 micrograms ```
33
Majority of T4/T3 in plasma is (free/bound).
Bound to TBG, albumin, or transthyretin
34
The metabolic rate of many tissues is determined by the (free/bound) fraction of T3/T4.
Free
35
T/F: Physiological thyroid status best correlates with T3/T4 that's bound to TBG, not albumin.
False - free hormone fraction
36
T/F: Thyroid hormones are transported into target cells via passive diffusion.
False - via membrane carriers
37
T/F: Rate-limiting step of thyroid hormone action is transport into target cell.
True
38
Once inside target cell, thyroid hormone binds (X) receptors, in conjunction with (Y).
``` X = non-histone protein nuclear receptors Y = TRE (thyroid hormone response elements) ```
39
List some proteins with genes that are regulated by T3.
1. T3's own receptor (and TRE) 2. TRH, TSH 3. GH 4. Myosin heavy chain
40
Certain tissues, such as (X), with (many/few) (Y), have significant response to T3 and large changes in protein synthesis/enzyme patterns.
X = liver Many; Y = nuclear receptors for T3
41
List the two key ways that myocardial tissues respond to T3.
1. Increasing adrenergic receptors | 2. Increasing actomyosin ATPase activity
42
T/F: Only the active thyroid hormone (T3) enters the target cell.
False - T4 enters too (encounters intracellular deiodinases that convert it to T3)
43
T/F: Only the active thyroid hormone (T3) enters the target cell nucleus.
True
44
T/F: Intracellular deiodinases (in target cell) only work on T4 (to produce T3).
False - also cleave T3 to T2/rT3 or T4 to rT3
45
T3 effect: (increase/decrease) bone formation/maturation.
Increase
46
T3 effect: (increase/decrease) oxygen consumption, BMR, and heat production.
Increase
47
T3 effect: (increase/decrease) CO and ventilation. (Up/down)-regulation of (X) adrenergic receptors.
Increase; Up-regulation; X = beta
48
T3 effect: increase in which processes in skeletal muscle?
Glycogenolysis and protein catabolism
49
T3 effect: increase cholesterol (synthesis/degradation) and (increase/decrease) LDL clearance/receptors.
Synthesis; | Increase
50
T/F: Thyroid hormone normally stimulates exclusively catabolic pathways.
False - both anabolic and catabolic pathways (supports balance)
51
T3 effect: there's a(n) (increase/decrease) in need for fuel. This is met by (increase/decrease) in which factors?
Increase; increase 1. GI motility/absorption 2. Increase appetite
52
T/F: Like sympathetic stimulation, TPR increases with increase in T3.
False - T3 increases production of vasodilatory metabolites and TPR falls
53
T/F: Normal whole body growth cannot occur without adequate T3 levels, even if GH is normal.
True
54
A hypothyroid child will have a bone age that's (more/less) than chronological age.
Less
55
Untreated (hyper/hypo)-thyroidism in children can lead to which brain impairment?
Hypo; | Severe, irreversible mental retardation
56
Fetal thyroid gland forms (early/late) in (X) trimester. By (Y) stage, the fetal hypo-pit-thyroid axis is fully operational.
Early; X = first Y = mid-gestation
57
During development, fetus receives (T3/T4/TSH) from mother/placenta to supply its needs. Thus, maternal (X) levels increase to meet greater demands.
T3 and T4; Iodide and thyroid hormone
58
The (increase/decrease) in thyroid hormone output during pregnancy is not met with (hyper/hypo)-thyroidism. Why?
Increase; hyper Increase in TBG (due to estrogen) to bind the increased hormone levels
59
Early in pregnancy, it's actually (X) hormone that stimulates thyroid to secrete.
X = hCG (not TSH)
60
First trimester of pregnancy: (increase/decrease) hCG, (increase/decrease) TSH, (increase/decrease) thyroid hormones.
Increase; Decrease (neg feedback from increased T3/T4); Increase (continued secretion stimulated by hCG)
61
Grave's disease is an example of (primary/secondary) (X).
Primary; | X = Hyperthyroidism
62
Exophthalmos is seen in (X) condition. What's the reason for this?
X = hyperthyroidism; Inflammation/swelling in orbital tissues (pushes eyeballs forward)
63
Hashimoto's disease is (primary/secondary) (X). What's the central issue in this disease?
Primary; X = hypothyroidism Anti-thyroid Ab (autoimmune); leads to eventual destruction of thyroid gland
64
What's the mechanism behind swelling of (X) gland in Hashimoto's disease?
X = thyroid Inflitration of lymphocytes as well as fibrosis
65
Silent, post-partum (X) condition begins with (hyper/hypo)-thyroidism, then (hyper/hypo)-thydroidism until normal function is reached again.
X = thyroiditis (inflammation of thyroid gland) Hyper; hypo
66
It's a "rebound" or (increase/decrease) in (X) function that causes post-partum thyroiditis.
Increase; | X = immune system

Endo/Repro (15 decks)

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